In general, an organic light emitting phenomenon indicates conversion of electric energy into light energy by means of an organic material. An organic electro-luminescence device using the organic light emitting phenomenon generally has a structure including an anode, a cathode, and an organic material layer interposed therebetween. Herein, in many cases, the organic material layer may have a multi-layered structure having respective different materials in order to improve efficiency and stability of an organic light emitting device. For example, it may include a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and the like.
When such an organic electro-luminescence device is applied with a forward voltage, holes and electrons are injected from an anode and a cathode, respectively. Then, the holes and the electrons recombine in a light emitting layer, thereby forming excitons (electron-hole pairs). When the excitons are converted from an excited state of pi-electrons per molecule to a ground state, the corresponding energy is converted into light. In order to enhance the color purity and efficiency of emitted light, there has been recently known a method for doping a small amount of a fluorescent or phosphorescent pigment into the light emitting layer forming excitons. The method is based on the principle that if a small amount of a fluorescent or phosphorescent pigment (hereinafter, referred to as a dopant) having a smaller energy band gap than molecules forming a light emitting layer is mixed with the light emitting layer, excitons which are generated in the light emitting layer are transported to the dopant, thus emitting a light having a high efficiency.
Various materials emitting green light, such as 8-hydroquinoline aluminum salt, have been conventionally used as a host. However, there are some problems to be improved in view of luminous efficiency and life span.